threads: give threads more time to get ready

threads: give threads more time to get ready

In certain conditions, it can take a long time for threads to start up.
For example in af-packet, setting up the socket, rings, etc has been
observed to take close to half a second per thread, and since the
threads go one by one in a preset order, this means the start up can
take a lot of time if there are many threads. The old logic would just
allow a hard coded 60s. This was not always enough when the number of
threads was high.

This patch makes the wait time take the number of threads into account.
It adds a second of time budget to the base 60s for each thread.

So as an example, if a system has 112 af-packet threads, it would wait
172 seconds (60 + 112) for the threads to get ready.

Ticket: #7048.
(cherry picked from commit 41b9836b11bbd653953f5c5dc5f87875e15fae8d)